Table 2.

Menstrual Cycle Characteristics and Time to Pregnancy, Denmark, 2007–2009

	No. of Pregnancies	No. of Cycles	Unadjusted Model		Adjusted Modela
			FR	95% CI	FR	95% CI
Menstrual cycle length, days
<25	65	646	0.60	0.46, 0.78	0.64	0.49, 0.84
25–26	152	996	0.92	0.77, 1.11	0.94	0.77, 1.13
27–29	1,051	6,411	1.00	Referent	1.00	Referent
30–31	416	2,321	1.10	0.97, 1.25	1.10	0.97, 1.25
32–33	92	419	1.40	1.10, 1.78	1.35	1.06, 1.73
≥34	87	467	1.17	0.92, 1.50	1.17	0.91, 1.49
Age at menarche, years
<12	245	1,424	1.04	0.89, 1.22	1.06	0.91, 1.24
12–13	1,056	6,420	1.00	Referent	1.00	Referent
14	376	2,158	1.07	0.94, 1.22	1.05	0.92, 1.20
≥15	186	1,258	0.89	0.75, 1.05	0.88	0.74, 1.05
Time until cycle regularity, years
<2	933	5,365	1.00	Referent	1.00	Referent
2–3	592	3,719	0.90	0.80, 1.02	0.90	0.80, 1.02
≥4	338	2,176	0.89	0.78, 1.03	0.89	0.77, 1.03
Duration of menses, days
<3	150	1,048	0.86	0.71, 1.04	0.87	0.72, 1.05
3–4	1,006	5,921	1.00	Referent	1.00	Referent
5–6	636	3,938	0.94	0.84, 1.05	0.92	0.82, 1.02
≥7	71	353	1.19	0.91, 1.56	1.14	0.87, 1.51
Intensity of menstrual flow
Light (≤10 pads/tampons)	449	2,814	0.94	0.83, 1.07	0.95	0.84, 1.09
Moderate (11–20 pads/tampons)	1,079	6,320	1.00	Referent	1.00	Referent
Heavy (21–30 pads/tampons)	313	1,936	0.91	0.76, 1.09	0.90	0.74, 1.08
Very heavy (>30 pads/tampons)	22	190	0.76	0.47, 1.22	0.70	0.43, 1.13
Menstrual flow and duration
Light/moderate, <5 days	1,052	6,263	1.00	Referent	1.00	Referent
Light/moderate, ≥5 days	104	706	0.84	0.66, 1.07	0.84	0.65, 1.09
Heavy/very heavy, <5 days	476	2,871	0.97	0.86, 1.10	0.95	0.84, 1.09
Heavy/very heavy, ≥5 days	231	1,420	0.94	0.77, 1.13	0.90	0.74, 1.09

Abbreviations: CI, confidence interval; FR, fecundability ratio.

^aAdjusts for age, body mass index, smoking, intercourse frequency, last method of contraception, and menstrual cycle length (when applicable).